A Home Brewed ST-5C Guider Interface

Having heard some horror stories from a friend about hooking up an SBIG camera to non-LX-200 scopes, I decided to slap together an isolated interface to the hand pad of my Mel Bartels telescope drive system.

The above circuit provides up to 7500v isolation between the two devices.  The NTE 3041 opto-islolator is the equivalent of the 4N36 and it's brethren (most of the differences between the  4N35,36,37 and such is the isolation voltage). 

The 470 ohm resistor was selected to limit the current on the input side to about 18ma with the LED having 2.2 V_F (Volts Forward) and the photo-diode having 1.5 V_F .

You must remove the cover from the ST-5C CPU and install jumper JP1 to supply 12 Volts at pin 6 of the guider port.

All of this was built into a small Radio Shack project box using  wire wrap sockets to hold the ICs.    I have my hand pad already paralleled with another relay board so I just used the screw terminal blocks to allow me to switch between the two.  You could just as easily use an RJ or Sub-D type connection for that end.

Here are photos of the completed project:

Component Side                                                                       Wiring Side

The schematic was drawn using Eagle 4.08r2 Light Edition

Disclaimer:

I am very comfortable modifying my own equipment, knowing full well the potential to cause serious damage to it.  This solution worked for me, your mileage may vary.  I cannot be held responsible for the accuracy of the information contained on this page or how you choose to use it!